This invention relates generally to a friction face assembly for a magnetic coupling such as a clutch or a brake and, more particularly, to an assembly of the type in which the friction face may be easily removed from the coupling and replaced with a new friction face when the friction face becomes worn.
An easily replaceable friction face for a magnetic coupling is disclosed in Kroeger et al U.S. Pat. No. 4,344,056. In that instance, the friction face is formed by a sheet of friction material having parallel faces and having inserts made of magnetic material and defining the active pole faces of the magnetic coupling. The friction face preferably is made by molding the friction material around the inserts such that the inserts are located in place by the friction material with opposite faces of the inserts disposed flush with the faces of the friction material. The friction face thus formed is detachably secured to a magnetic mounting plate of the coupling and, when wear occurs, the entire friction face (i.e., the friction material and the inserts) may be easily removed and replaced.
In heavy duty couplings with high torque capacity, prior inserts tend to skew within the friction material due to differential expansion, high pressure and the like. Such skewing tends to create air gaps in the magnetic circuit and thereby reduces the efficiency of the coupling. Under extremely heavy duty service, prior inserts tend either to work loose from the friction material or to cause flexing of the friction material, tend to wear faster than the friction material and tend to pull away from the mounting plate. As a result, air gaps detrimental to the efficiency of the coupling are created between the inserts and the mounting plate and, in addition, the inserts and the friction material experience uneven wear.